By means of soles, shoes are provided with a variety of different properties that may, depending on the specific type of shoe, be realized to different extents. Primarily, shoe soles usually serve protective purposes. By means of their stiffness, which is increased when compared to the stiffness of the shoe upper, shoe soles protect the respective wearer's foot from injuries caused for example by sharp objects that the wearer of the shoe steps upon. Moreover, a shoe sole usually protects the shoe from excessive abrasion by means of its increased abrasion-resistance. Further, shoe soles may increase the grip of a shoe on the respective ground and may thus facilitate quick movements. It may be a further function of a shoe sole to provide a certain stability. In addition, a shoe sole may provide a cushioning, for example to damp the forces that occur when the shoe contacts the ground. Finally, a shoe sole may protect the foot from dirt or splash water or it may provide a multitude of further functionalities.
In order to meet this plethora of functionalities, various materials are known in the prior art out of which shoe soles may be manufactured. For example, shoe soles may be manufactured from ethylene-vinyl acetate (“EVA”), thermoplastic polyurethane (“TPU”), rubber, polypropylene (“PP”) or polystyrene (“PS”). Each of these different materials provides a specific combination of different properties that are more or less well suited for soles of specific types of shoes, depending on the particular requirements of the respective type of shoe. For example, TPU is very abrasion-resistive and tear-resistant. Moreover, EVA provides a high stability and relatively good cushioning properties.
It is a common disadvantage of the aforementioned materials that shoe soles made from of these materials have to be manufactured separately and subsequently have to be attached to the shoe upper, e.g. by gluing or sewing. From WO 2008/087078, WO 2007/082838, WO 2010/136398, and WO 2005/066250, expanded TPU is known, which may be used for manufacturing shoe soles. For example, WO 2005/066250 describes that a shoe sole formed out of expanded TPU may be attached to a shoe upper without additional gluing means. Further, WO 2005/066250 discloses that the expanded TPU is foamed in a tool in contact with the shoe upper and, thus, a sole made of expanded TPU is provided that adheres to the shoe upper. In addition, WO 2005/066250 describes the possibility of pre-manufacturing an outsole of thermoplastic elastomer (e.g. polyvinyl chloride (“PVC”), thermoplastic rubber, TPU) and, after its curing, providing expandable TPU in the form of foam to a cavity between the outsole and the shoe upper. Hence, the outsole does not need to be glued to the shoe upper.
However, the disclosure of WO 2005/066250 describes the disadvantage that the properties of the sole are influenced by the sole of expanded TPU continuously over the entire surface. A fine control of the sole properties is not possible according to WO 2005/066250.
It is therefore desirable to provide improved soles for shoes, in particular sports shoes. It is further desired to provide improved possibilities to construct such soles from expanded TPU.